Di(sec-alkyl)-p-phenylenediamines are powerful antioxidants and antiozonants for the preservation of diene rubber. Higher members of 7 or 8 carbon alkyl groups having high antioxidant and antiozonant properties, acceptable low volatility and low skin burning effect are produced from ketones of 7 or 8 carbon atoms and have become widely accepted in the rubber industry. The high antidegradant activity, availability and economy of the raw materials recommend lower alkyl groups. However, the lower members of the series are volatile skin irritants with the result that not only are they rapidly lost from the rubber with resultant loss of preservative action but cause serious discomfort to workmen. Moreover, rubber preserved with the 6 carbon atom alkyl compound, N,N'-di(1,4-dimethylbutyl)-p-phenylenediamine, gives evidence of being a skin sensitizer. The ability of an agent to elicit a primary skin irritation is wholly different from that of producing skin sensitization.